As the instrument panel for an automobile, there have heretofore been used those in which a skin material is laminated with an adhesive to a thermoplastic resin core material previously formed into the desired shape by injection molding or the like.
Usually, such instrument panels for automobiles are required to have an opening portion such as an air blowoff hole for air-conditioning or preventing window glass from being clouded, or the like, and as an instrument panel having such an opening portion, there have been known those in which an opening portion consisting of a single opening having the desired size is provided by mechanically boring or the like in an instrument panel in which a skin material is laminated to the whole surface of a resin core material and which has been obtained by a method as mentioned above and those obtained, when an opening portion consisting of a plurality of small holes is required, by fitting an opening part having at least 2 plural small holes formed separately by injection molding or the like to the said opening portion and fixing the part in the opening portion.
However, in the heretofore known instrument panels, there have been such problems that the bonding strength between the thermoplastic resin core material and the skin material is insufficient, that since an opening portion is provided by boring mechanically or the like a panel as obtained by laminating the skin material to the resin core material, the end of the skin material layer rises onto the panel surface at the bored panel face around the opening portion to mar the beauty remarkably and that when the opening portion is composed of small holes the separately formed opening part is fitted to and fixed in the opening portion and hence the fitting strength of the opening part to the opening portion is insufficient, whereby the opening part comes up or disconnected from the opening portion owing to vibration during the running.